Neuro Chapter 10

9. Are there practical applications of the gate control theory of pain?

The gate control theory is applied when area of the body feels pain and a person rubs that area. (example stubbed toe) The rubbing is thought to relieve pain because the neurons responding to the non-painful rubbing out competes the neurons signaling pain. To propose that the flow of nociceptive information through the spinal cord is modulated by concomitant activation of the large myelinated fibers associated with low-threshold mechanoreceptors.

transient receptor potential (TRP)

Also known as vanilloid receptors. They are found in both C and Aδ fibers, ones with higher thresholds are found only in Aδ fibers. These are channels that closely resemble voltage gated potassium channels. The channel is closed at resting potential, they open when activated via heat (or capsaicin) allowing an influx of sodium and calcium that initiates the generation of action potentials in the nociceptive fibers.

4. Give an example of referred pain and offer a possible explanation.

An example of referred pain is when a patient is passing a kidney stone, can be referred to the lower abdominal wall. Also a heart attack, pain is coming from the heart muscle but pain is felt in the left arm and neck. Referred pain is when pain typically occurring from an internal organ is felt in a different part of the body. The cause may be from there are few, if any, neurons in the dorsal horn of the spinal cord that are specialized solely for the transmission of visceral pain. Obviously, we recognize such pain, but it is conveyed centrally via dorsal horn neurons that are also concerned with cutaneous pain. This is a "mix up" of somatosensory neurons, because they travel on the same tracts (heart, neck, arm) (kidney, lower abdominal sensation).

anterolateral system

Anterolateral system is a pathway in which the signal from the nociceptor reaches the brain. It is made up of three major pathways, but the book only mentions the spinothalamic tract which is involved in the awareness and recognition of where the pain stimulus is happening in the body. The pathway involves nociceptor synapses in the spinal cord -> second neuron that crosses to the other side of the spinal cord before traveling up -> this tract travels to the ventral posterior nucleus in the brain which synapse -> this next neuron sends the pain information to the somatosensory cortex.

wide-dynamic-range neurons

Axons in lamina 5 ("wide-dynamic-range neurons") receive both superficial and visceral input, making them likely sources for referred pain.

7. Why do chili peppers seem hot?

Certain nociceptors are both sensitive to heat and capsaicin (a chemical found in peppers). When capsaicin binds to the nociceptor it activates the same response that would occur as if it were activated by high temperature. The brain gets the same signal from heat that it does from capsaicin, this is why pepper seem to be hot.

endogenous opioids

Endogenous opioids are an opioid like substance that is naturally produced by the body.

1. What is the evidence that nociception is mediated by specific nociceptors rather than by strongly stimulated tactile receptors or warm receptors?

Experimental demonstration that nociception involves specialized neurons, not simply greater discharge of the neurons that respond to normal stimulus intensities. So it's not as if when the heat receptors get a stimulus past a certain point they start to signal pain, rather the nociceptors responding to heat are totally separate and have a much higher threshold that signals the potential for tissue damage.

first pain

First pain is a type of pain perception. It is sharp pain, signaling to you in a half second or less. It is the response given to remove your hand from a hot object, initiating immediate motor response. gate theory of pain

placebo effect

Is a physiological response following the administration of a pharmacologically inert "remedy." Meaning when people receive a treatment that should have no effect, if the person believes that there will be an effect there could be actual physiological responses.

allodynia

Is the induction of pain by what is normally an unharmful stimulus. This phenomenon typically occurs immediately after the painful event and can outlast the stimulus by several hours.

peripheral sensitization

It is when cell and tissue become damaged they release chemicals that induce the inflammatory response. The inflammatory chemicals interact with the nociceptors' receptors and ion channels which increases the response of the nociceptors. The response of the nociceptors binding to certain inflammatory chemicals causes the nociceptors to release chemicals that further increase the response by creating vasodilation, as well as making it so that the nociceptor is more sensitive and can respond to stimuli at a lower threshold. Big picture: that nociceptors are a key part in the inflammatory response because not only does it aid in the signalling for responses that help with healing (increase vasodilation, swelling), it also signals to the brain to avoid pressure to the already injured area.

8. The placebo effect on pain can be blocked by naloxone. What does this observation reveal about the pain system?

Naloxone, a competitive antagonist of opiate receptors, indicating a substantial pharmacological basis for the pain relief experienced. A common misunderstanding about the placebo effect is the view that patients who respond to a therapeutically meaningless reagent are not suffering real pain, but only "imagining" it; this is certainly not the case. This means the placebo effect actually causes physiological changes in the body that can block pain, and that other chemicals can block that.

nociceptors

Nociceptors are a unspecialized nerve cell endings that initiate the sensation of pain. They respond to noxious stimuli like extreme pressure, hot or cold, or tissue damage.

3. Due to a spinal injury, a patient has lost pain and temperature sensation on the left half of his body from the waist down. Where is his injury? Where would you expect loss of tactile sensation in this patient?

Pain and temperature neurons cross the midline of the spinal cord, meaning that if loose of sensation occurs on the left side, the damage must of occurred on the right side. You would expect the loss of pressure, touch, vibration, and proprioception to be lost on the right side, same side that the damage occurred, because theses neurons do not cross the midline of the spinal cord.

second pain

Second pain is a type of pain perception. It is dull or emotional pain. It comes on slowly and sticks around for longer. This is the pain that tells your brain not to repeat the same activity that caused the pain in the first place.

6. Is phantom limb pain less "real" than pain from an intact limb?

That depends on what you consider less real. Phantom pain is still pain. Phantom sensations (including pain) apparently result from a remapping of sensory cortex in the absence of afferent sensation, such that novel areas of stimulation are actually mapped into the area where no other stimuli arrive.

2. Are hyperalgesia and allodynia beneficial? Summarize the contributions of peripheral and central sensitization.

They are beneficial in the sense that they make the tissue that has been damaged even more sensitive to pain, by doing this it create a behavioral response that keeps that person from damaging the tissue further.

central sensitization

This involves the central nervous system (brain and spinal cord), where the threshold for pain is decreased allowing for pain to remain for a longer period of time and allowing for smaller stimuli to induce a pain response.

dissociated sensory loss

This is the loss of sensation do to spinal damage. Since the sensations of touch, pressure, vibration and proprioception travel up the same side that the sensation occurs on, if you damage that side of the spinal cord, that side will loose those sensations. But the sensations of temperature and pain cross the midline of the spinal cord before ascending meaning, if those were damaged, there would be a loose of sensation on the opposite side of the body that the damaged occurred on. This patterned is referred to as dissociated sensory loss.

11. What are the three major groups of endogenous opioids?

Three major groups of endogenous opioids are Endorphins, Enkephalins, and Dynorphins

dorsolateral tract of Lissauer

When the nociceptors nerve cells reach the dorsal root of the spinal cord, they split into ascending and descending collaterals, this nerve fiber is what makes up the dorsolateral tract of Lissauer. These tracts typically only run the length of one or two spinal cord segments before going into the spinal cord's gray matter.

neuropathic pain

a chronic, intensely painful experience that is difficult to treat with conventional analgesic medications. When patients with neuropathic pain have unharmful stimuli like touch of clothing or slight change in temperature they gain a intense pain response of intense burning sensation, and/or episodes of sharp stabbing pain. This is thought to be caused when the afferent fibers or central pathways themselves are damaged. This can occur in shingles, diabetes, AIDS, multiple sclerosis, or stroke.

Aδ group

is one of the classes of axons for nociceptors fall into. This class has a myelinated axon and can conduct its signal faster, it is associated with fast and sharp pain.

C fiber group

is one of the classes of axons for nociceptors fall into. This class has an unmyelinated axon and conducts its signal slower than Aδ afferents. These neurons are associated with second pain, one that comes on slower, dull and emotional pain.

dynorphins

one of the three major groups of endogenous opioids.

endorphins

one of the three major groups of endogenous opioids.

enkephalins

one of the three major groups of endogenous opioids.

hyperalgesia

stimuli in the area of the injury and the surrounding region that would ordinarily be perceived as slightly painful are perceived as significantly more so, an example of this is sunburn